Prior to the present invention, curable silicone emulsions providing an elastomer upon water removal were shown by J.F. Hyde et al., U.S. Pat. No. 2,891,920. It was found that the compositions of Hyde et al. required either a strong acid or a strong base to achieve stability of the emulsion. As a result, Hyde et al.'s silicone emulsions were limited in use due to their adverse effects on various substrates. Improved results are shown by D. E. Findlay et al., U.S. Pat. No. 3,294,725, employing a surface active sulfonic acid catalyst to achieve a stable emulsion and allow for the copolymerization of organosiloxanes and silacarbanes. An additional procedure for making silicon rubber latexes is shown by J. Cekada, Jr., U.S. Pat. No. 3,355,406, utilizing silsesquioxanes to reinforce the polymer.
The present invention is based on the discovery that stable aqueous curable silicone latex compositions can be made by initially emulsifying silanol-terminated polydiorganosiloxane in the presence of a nonionic surfactant, such as an alkylaryloxypoly(ethyleneoxy)ethanol followed by a pH adjustment up to 5 with a carboxylic acid, such as succinic acid. Also used in the emulsion are alkyltrialkoxysilane, for example methyltrimethoxysilane and a tin catalyst, such as a stannoxane, hydroxystannoxane, or a monomethoxy tin compound. Among the preferred tin compounds are stannoxanes of the formula, EQU (R).sub.2 SNX-O-Sn(R.sup.1).sub.2 OH, (1)
where R and R.sup.1 are selected from the same or different C.sub.(1-8) alkyl radicals, and preferably butyl, and X is a halogen radical, or an acyloxy radical, and is preferably chloro.
In addition, calcium carbonate is utilized in the resulting curable silicone composition. The resulting silicone caulk has been found to have superior shelf life, such as six months or more, and elastomers resulting from the removal of water from such caulking compounds have been found to have excellent physical properties.